It is not a particularly cutting-edge study. But since its focus is human CAR-T cells such limited experiments are still expected. Though I will anticipate that soon publications of in vitro studies on human primary cells [in top journals] will require incorporation of specific gene targeting experiments using CRISPR-Cas9 technology. Such experiments are now technically feasible and will be more informative.

In short, for this study the authors compared proliferation/expansion and metabolic/energy source of two CAR constructs, one with CD28 and another with 4-1BB (aka CD137) signaling domains, as shown below. FMC63 is anti-CD19 scFv and SS1 is anti-mesothelin scFv.

Human primary T cells were electroporated with these two CAR constructs. Efficacy of CAR expression was 90%.